1. Field of the Invention
The present invention relates to spin MOSFETs.
2. Related Art
In recent years, intensive studies are being made to develop devices such as spin MOSFETs having novel functions. One of those devices is a spin MOSFET that has the source-drain region formed with a magnetic material. Such a spin MOSFET is characterized in that the output characteristics can be controlled simply by reversing the spin moment direction of the magnetic material of the source-drain region. This feature can be utilized to form spin MOSFETs that have amplifying functions as well as reconfigurable functions, and to form a reconfigurable logic circuit with those spin MOSFETs.
To put such spin MOSFETs and a reconfigurable logic circuit having amplifying functions as well as reconfigurable functions into practical use, it is necessary to overcome the following two problems.
One of the two problems is to be eliminated by reducing the current when writing is performed and the spin moment direction of the magnetic material of the source-drain region is reversed, and the other one is to be eliminated by increasing the change in output characteristics observed when the spin moment direction is reversed.
To solve the first one of the problems, a writing method utilizing spin injection has been suggested (see the specification of U.S. Pat. No. 6,256,223, for example). A spin reversal can be performed by spin-injecting a spin-polarized current. However, in a case where this spin injecting technique is applied to a spin tunnel device, a problem of a defective device is caused by breakdown of the tunnel insulating film, for example. This reduces the reliability of the device. Also, to maintain reasonable scalability, which is an ultimate objective, a spin injection reversal should be performed at a low current density in a structure that is not affected by a heat fluctuation when the structure is made smaller.
Therefore, it is necessary to provide a spin memory that maintains a low current density so as not to cause breaking of the device at the time of writing by the spin injecting technique, exhibits high resistance to heat fluctuations, and performs a spin reversal at a low current density.
To solve the second problem, the use of a half-metal material for the magnetic material has been suggested (see APL84 (2004) 2307, for example). Where such a half-metal material is employed, a sufficient output difference is not achieved, and a larger increase in the output difference is expected.
As described above, a spin MOSFET structure that performs a spin reversal at a low current density and achieves large output characteristics through the spin reversal has not been produced yet.